1. Field of the Invention
The present invention relates to a seat belt retractor provided with a belt tension eliminating mechanism capable of relieving belt wearers from body-squeezing tension. More particularly, the present invention relates to a seat belt retractor provided with an improved belt tension eliminating mechanism which enables freely protracting the seat belt under normal seating conditions so as to relieve the belt wearer from body-squeezing pressure caused by tension of the belt and retracting an excess length of the seat belt to the memory position previously determined by pulling out the seat belt slightly after the seat occupant fastens it.
2. Description of the Prior Art
In recent years, the use of a seat belt has legally been required for seat occupants in automobiles in many countries for the purpose of preventing injury or physiological damage caused by a traffic accident. Thus, a great number of seat belt assemblies have been proposed hitherto for this purpose. Most of the seat belt assemblies now proposed are provided with a seat belt retractor which is cooperated with an electromagnetic plunger device associated with buckle parts of the seat belt and is designed to enable pulling out the seat belt by the belt wearer under normal seating conditions thereby reducing the body-squeezing pressure caused by tension of the seat belt. Basically, a conventional seat belt retractor comprises a solenoid plunger, a shaft and a reel as a belt-winding device, a rachet plate simultaneously rotatable with the reel, a pawl engageable with the rachet, a spring acting in the direction of rewinding the belt and a rotatable member co-rotatable with the rachet plate under normal conditions. When a seat occupant wears a seat belt by joining the buckle parts of the belt, a switch fitted to the buckle parts is turned on to send an electric current to the solenoid whereby the rachet plate is engaged with the pawl by the action of the plunger to inhibit the rotation of the reel in the direction of rewinding the belt. In this state, the belt-rewinding force is not exerted but the rotatable member allows pulling out the belt while overcoming resistance to the force of the spring pulling back the belt to the reel. These seat belt retractors proposed heretofore which are greatly or slightly different in structure from one another satisfy the belt-protracting and -retracting functions to a certain degree but still have a number of drawbacks to be overcome.
In a seat belt retractor disclosed in Japanese Patent Publn. No. Sho. 55-51583 (U.S. Pat. No. 4,172,568), for example, the belt rewinding device comprises a shaft 6 (28 in the U.S. patent) and a reel 18 (26) while the rachet plate and the pawl are constructed by a disk rachet 25 (a rachet wheel 60) and a stopper 40 (a lever 92), respectively. The stopper 40 (the lever 92) is engageable with the disk rachet 25 (the rachet wheel 60) by the action of a solenoid 44 (an electric actuator 102). The rotatable member is constructed by an external gear 30 (a planetary gear 64) and is connected to the disk rachet 25 (the rachet wheel 60) by a spring 35 (a spring 78) in such manner that a stud 33 (68) may be engaged with the end 28 (70a) of a slot 28 (70) formed in the external gear 30 (64) by the action of the spring 35 (78). An eccentric part 22 (an eccentric bearing portion 58) of the reel 18 (26), the external gear 30 (the planetary gear 64) and an internal gear 36 (84) form a cycloid revolution-decreasing mechanism. In this seat belt retractor, the locus of the movement of the external gear 30 (the planetary gear 64) in the cycloid revolution-decreasing mechanism, especially the locus of the movement of the stud 33 (68) in the slot 28 (70) in the event the disk rachet 25 (the rachet wheel 60) is stopped by engagement with the stopper 40 (the lever 92), depicts a hypoinferior-trochoidal curve thereby generating a reverse component moving in the opposite direction to the generally progressing direction. Thus, the position of the stud 33 (68) at the end 28b (70a) tends to migrate, resulting in such a drawback that the memory position of the seat belt may fluctuate to impart uncomfortable pressure to the belt wearer.
Japanese Patent Publn. Nos. Sho. 56-3060 and 56-41258 (U.S. Pat. No. 4,228,971) disclose seat belt retractors improved in this respect. The retractor disclosed in the former publication is designed to have such a structure that a stud 25 (44) is located in a projected position (42b) outside the addendum circle of the external gear 20 (42) so that the locus of the stud in a slot 22 (40b) of a disk rachet 20 (a rachet wheel 40) may depict a hyposuper-trochoidal curve to prevent the generation of the above mentioned reverse component. The other one disclosed in the latter publication is designed to have such a structure that a plurality of studs 25a, 25b and 25c (44'a, 44'b and 44'c) positioned in projections (42'b-a, 42'b--b and 42'b-c) and a plurality of slots 22a, 22b and 22c (40'b-a, 40'b--b and 40'b-c) are so arranged that at least one stud may be brought into contact with the ends of the slots in a position other than that where the reverse component is formed. As compared with the seat belt retractor disclosed in Japanese Patent Publn. No. Sho. 55-51583, these seat belt retractors can determine the memory position exactly but have a drawback that the length of the seat belt capable of being pulled out beyond the memory position is limited so that the seat occupant cannot move his body freely after wearing the seat belt.
On the other hand, an improvement is also proposed to increase the length of the seat belt pulled out beyond the memory position. In a seat belt retractor disclosed in Japanese Laid-open Patent Appln. No. Sho. 54-100023 (U.S. Pat. No. 4,199,172), a shaft 2 (20) corresponding to the reel and a carrier 24 (a discal carrier 70) corresponding to the rotatable member are constructed to form a revolution-decreasing (i.e. reduction gear) mechanism wherein a planetary gear is used intermediately. More precisely, this revolution-decreasing mechanism comprises a sun gear 29 (84) fixed to the shaft 2 (20), a planetary gear 28 (82) supported by the carrier 24 (the discal carrier 70) and engaged with the sun gear 29 (84), and a fixed internal gear 31 (86) engaged with the planetary gear 28 (82) and freely provides a revolution-decreasing ratio by properly designing the number of teeth of the gears. This mechanism enables pulling out the seat belt until the carrier 24 (the discal carrier 70) rotates by one revolution relative to a first gear 13 (an external gear 62) so that the length of the seat belt pulled out is longer than in the case of the above mentioned publications. However, this seat belt retractor has also a detrimental drawback because the belt-rewinding force is not exerted as soon as the seat occupant has worn the seat belt. On using the seat belt, the seat occupant will normally pull out the seat belt in a slight excess for facilitating his buckling operation. In such case, the seat belt is fastened in a somewhat loosened state and the position where the belt-rewinding force is cancelled is memorized in this state, thus resulting in a danger that the belt wearer may not sufficiently be restrained with the seat belt when any emergency such as a crash occurs.
Recently, seat belt retractors further improved to overcome the above drawbacks are proposed in Japanese Laid-open Patent Appln. No. Sho. 56-128248 and Japanese Laid-open Patent Appln. No. Sho. 56-124532 (U.S. Pat. No. 4,456,196). In the seat belt retractor disclosed in the first mentioned publication, (A) a rewinding mechanism (for preventing the loosening of the seat belt) is constructed by a disk 3, a friction plate 4, a stopper pin 14, a spring 6, a stopper arm 10 and a rotation-preventing stopper 8 and (B) a controlling mechanism (for the above mechanism (A)) is constructed by the stopper arm 10, the rotation-preventing stopper 8 and the stopper pin 14. In the seat belt retractor disclosed in the last mentioned publication, the mechanism (A) is constructed by a clutch plate 8 (a clutch disk member 48), a spring 9 (a disk spring 52), a first projection 81 (a first outwardly extending arm 54) of the clutch plate 8 (the clutch disk member 48), pins 9 and 9' (stopper pins 58 and 60) and a second projection 82 (a second outwardly extending arm 56) of the clutch plate 8 (the clutch disk plate 48) among which the first projection 81 (the first outwardly extending arm 56) and the pins 9 and 9' (the stopper pins 58 and 60) comprises the controlling mechanism (B). In these seat belt retractors, the seat belt can be pulled out beyond the memory position while the loosened excessively pulled out seat belt or slack can be rewound so that most of the drawbacks mentioned above are overcome. Fully required for the seat belt retractors of this type under normal seating conditions are exact memory of a position of the seat belt where the belt-rewinding force is cancelled and free forward or backward movement (protraction or retraction ) of the seat belt from/to the memory position for preventing any loosening of the seat belt and assuring free movement of the user once he has worn the seat belt. However, all of the above requirements are not fully satisfied even by the seat belt retractors of the lastly mentioned type over all the possible occasions encountered under the normal seating conditions. When a seat occupant removes the position of his seat in forward or backward direction after wearing the seat belt, there may be a situation wherein he may feel body-squeezing pressure caused by belt tension since the position of the seat belt where the belt-rewinding force is cancelled has been memorized before removal of the seat. For example, the seat belt retractor disclosed in Japanese Laid-open Patent Appln. No. Sho. 56-124532 (U.S. Pat. No. 4,456,196) changes from the state as shown in FIG. 7 immediately to the state as shown in FIGS. 9 and 2 after wearing the seat belt whereby the position of the seat belt where the belt-rewinding force is cancelled is memorized. When the seat is moved forward while the seat belt retractor is in the state as shown in FIG. 7, a certain length of the seat belt is pulled out beyond the memory position so that the retractor changes not to the state as shown in FIG. 8 but to the state as shown in FIGS. 9 and 2. After the seat has been moved forward, therefore, the belt-rewinding force is exerted by the action of the memory spring 8' (a spiral spring 46) to the seat belt up to the position where the belt-rewinding force is cancelled which has been memorized prior to the movement of the seat. Thus, an increased belt tension is applied to the belt wearer after he has moved the seat. In view of the above situations, a new function is required for the seat belt retractors, which enables them to determine the memory position by pulling out the belt after wearing the seat belt, retracting the belt and then pulling it out again. In connection with the above, a second new function is required for the seat belt retractor. The seat belt retractor must be able to determine the memory position of the seat belt at the finally fastened stage, when the seat occupant once fastened the seat belt but unfastened and again fastened it for some reason. In the seat belt retractor disclosed in the above mentioned Japanese Laid-open Patent Appln. No. Sho. 56-124532 (U.S. Pat. No. 4,456,196), for example, the memory position is determined in the state as shown in FIG. 2. When the seat belt is taken off and again fastened immediately, or in other words, when a switch for a solenoid plunger 14 (a solenoid 92) is once turned off and again turned on immediately, a stopper 13 (a pawl member 62) is removed in the right direction in the drawing and again removed in the left direction whereby the engagement of a nail 10 (a detent 64) with an external gear 7 (an annular rachet wheel 38) may be kept throughout the operations. In particular, when the belt-wearing operation is repeated immediately, such engaged state is kept continuously so that the position determined at the initial wearing operation is again memorized even after the second wearing operation. It is a matter of course that the belt-rewinding force applied to the belt wearer is changed in such case. This phenomenon is remarkable when the external gear 7 (an annular rachet wheel 38) has a rachet structure as seen in the seat belt retractor of this example since the rotation of the external gear 7 (the annular rachet wheel 38) in the belt-rewinding direction is disturbed by the nail 10 (the detent 64) acting in the direction of inhibiting the rotation of the external gear so that the external gear and the nail are not easily released from engagement.
As is evident from the foregoing description and comparison, the seat belt retractor disclosed in Japanese Laid-open Patent Appln. No. Sho. 56-124532 (U.S. Pat. No. 4,456,196) belongs to the most advanced type but still further improvements are found necessary therefor in view of the above mentioned drawbacks and incorporation of the two new functions into its tension eliminating mechanism is also required for the seat belt retractor of this type. In the practical aspect, therefore, there is a great demand for developing a seat belt retractor which is improved fully in its tension eliminating mechanism and satisfactorily overcomes the above mentioned drawbacks.